Illumination devices based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting units that enable a variety of lighting effects in many applications. Some lighting units feature one or more light sources, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects.
Because of their small size and low-cost, simple linear driver circuits have generated considerable interest in field of the LED drivers. One of the biggest concerns regarding LED lighting is light flicker that can be perceived by the human eye. Because LEDs have a very fast dynamic response, energy storage is often employed to bridge the fluctuation in the instantaneous input power (50 Hz or 60 Hz “mains” voltage), in order to reduce flicker. This is typically achieved by adding large electrolytic capacitors at the primary and/or secondary side of the driver. In view of the fact that the dynamic resistance of an LED reduces as the LED efficiency improves, flicker reduction becomes more challenging for a space-constrained driver. Most existing LED drivers have a predominant frequency component in the LED light/current at twice the mains frequency (i.e., at 100 Hz or 120 Hz), where the human eye is sensitive to the modulated light.
On the other hand, at frequencies above 200 Hz, the human eye is much less sensitive to the modulated light (10 Hz being the most sensitive). Therefore, if a driver can be made with predominant AC component in the light output at 200 Hz or above, the perceived light flicker will be substantially reduced or eliminated, though light modulation still occurs.
Thus, there is a need in the art to provide a driver for a light source, and particularly an LED light source, which can reduce or eliminate visible flicker.